1. Field of Invention
The present invention relates to an improvement in a rotary tool such as an impact wrench and an impact driver for use in an operation to tighten a bolt, a nut and a screw.
2. Related Art
An impact rotary tool such as an impact wrench and an impact driver is a tool structured such that a hammer, which is connected through a cam to a drive shaft disposed so as to be rotationally driven, is energized by a spring to the side of an anvil disposed on an output shaft, and the anvil is engaged with the hammer in an impact manner by the cam and spring to thereby produce a rotational force; and, when it is used in an operation for tightening a bolt, a nut, and a screw, the impact rotary tool produces only a small reactive force which is given to the hand of an operator, and thus the impact rotary tool provides a high efficiency in the tightening operation. However, since the impact rotary tool produces an intermittent impact rotational force, in the case of making a hole in metal (in case where it is used as a drill), a drill bit can chip or the rotating number of the impact rotary tool can decrease, which makes it impossible to make a hole.
In view of this, there is proposed an impact rotary tool structured such that the motion of the hammer in the axial direction thereof is limited to thereby unable to provide an impact operation, that is, the hammer is prevented from parting away from the anvil to thereby be able to cope with a drill operation. However, in this case, in case where the restriction of the axial motion of the hammer is carried out by an external operation portion, there is still left a problem that the axial motion of the hammer by the spring is given to the-external operation portion to thereby lower the power transmission efficiency.
Here, in Japanese Patent Publication Hei. 7-40258, there is disclosed an impact rotary tool structured such that an anvil supported rotatable with respect to a drive shaft is connected to the drive shaft to thereby disable the anvil from rotating with respect to the drive shaft, that is, connect the anvil directly with the drive shaft, so as to be able to provide an operation which is different from the impact operation. In the case of this structure, there is eliminated the need to move the axial positions of the hammer and anvil against a spring used to energize the hammer, which makes it possible to switch a drill operation and an impact operation over to each other without lowering the power transmission efficiency.
In the impact rotary tool disclosed in the above-cited publication, however, to disable the anvil, which is supported rotatable with respect to the drive shaft, from rotating with respect to the drive shaft is carried out by inserting a connecting member into both of the drive shaft and anvil from outside. This makes it necessary for an operator to carry the connecting member and, in case where the connecting member is not available, it is not possible to switch the present impact rotary tool over to the drill operation.
In the above-cited publication, there is also disclosed an impact rotary tool which can be switched between the impact operation and the drill operation by moving an anvil in the axial direction thereof by means of an external operation. In this case, however, not only there is required a structure capable of moving the anvil in the axial direction thereof but also it is necessary to secure a space for the axial movement of the anvil, which increases the size of the drive portion of the impact rotary tool. Therefore, it is difficult to reduce the size of the impact rotary tool, and it is also difficult to use of the impact rotary tool in common with other tools which do not have the above-mentioned switching function.
Also, because the engagement between the drive shaft and anvil is impossible if the engagement portion of the drive shaft and the engagement portion of the anvil do not correspond to each other, it is necessary to match the positions of these two parts to each other.
Further, when the hammer stops in a state where the projecting portion of the hammer and anvil are superimposed on each other, in case where the drive shaft is connected to the anvil at this position, the load of the spring applied to the hammer acts as a rotation load to thereby lower the power transmission efficiency.
In addition, although the present impact rotary tool is able to make a hole as a drill, it does not employ a torque clutch or a speed change mechanism which are employed in an electric driver, because the employment of them incurs a further increase in the size of the impact rotary tool. This raises another problem in the impact rotary tool that tightening with a proper torque is impossible and a rotary torque is short, thereby being unable to carry out a satisfactory tightening operation.
The present invention aims at eliminating the above-mentioned drawbacks found in the conventional impact rotary tools. Accordingly, it is a main object of the invention to provide an impact rotary tool which can be simply switched between an impact operation and a drill operation and can prevent mechanisms necessary for execution of such simple switching from incurring an increase in the size of the impact rotary tool. Also, it is another object of the invention to provide an impact rotary tool which not only can realize a smooth switching operation but also is capable of employing a torque clutch and speed change means as well.
In attaining the above objects, according to the invention, there is provided an impact rotary tool, comprising:
an impact mechanism including a spring for energizing a hammer connected through a cam to a drive shaft toward an anvil disposed on an output shaft, the impact mechanism being structured such that the anvil is engaged with the hammer in an impact manner using the cam and spring to thereby be able to generate a rotation force; and,
switching means for switching the anvil supported relatively rotatable with respect to the drive shaft into a state in which the anvil is disabled from proportionally rotating with respect to the drive shaft,
wherein, in both of the drive shaft and anvil supported relatively rotatable with respect to the drive shaft, there are respectively formed engagement portions engageable with a connecting member, the connecting member is structured such that it can be operated in linking with the operation of an external operation inputting operation portion formed so as to be operated from outside, and the connecting member is used as the switching means.
According to the invention, in case where the external operation inputting operation portion is operated, the connecting member changes the state of the relative rotation relation between the drive shaft and anvil to thereby be able to switch the impact operation and drilling operation over to each other.
In this case, preferably, the engagement portion of the drive shaft and the engagement portion of the anvil may be situated on the same axis, and the connecting member can be switched between a state in which the connecting member is engaged with both of the two engagement portions of the drive shaft and the anvil at the same time and a state in which the connecting member is not engaged with at least one of the two engagement portions. And, in case where an intermediate transmission member interposed between a motor and said drive shaft is supported in such a manner that it can be freely moved in the axial direction thereof, and an operation member and the connecting member are connected to the present intermediate transmission member which is rotationally connected to the drive shaft through key connection, or in case where the intermediate transmission member and connecting member are connected to each other by a switching pin which extends through the drive shaft in the axial direction thereof and can be freely moved in the axial direction thereof with respect to the drive shaft, there can be obtained a special advantage that the impact rotary tool can be made compact.
And, preferably, the connecting member may be connected in such a manner that it can be freely rotated with respect to the switching pin and is disabled from moving in the axial direction thereof. Also, preferably, the switching pin includes a shaft which is supported at the axis position thereof by a member fixed to the motor.
Also, preferably, a torque clutch may be disposed in a power transmission route extending from a motor for driving to an output shaft. In this case, preferably, the present torque clutch may include an adjust screw which is supported threadedly movable back and forth for setting a sliding-start torque, and the adjust screw may be structured such that it can be engaged in an axially slidable manner with a drive portion cover disposed so as to be freely rotatable around its own axis with respect to a housing and the axial movement of the adjust screw can be achieved by the rotational operation of the drive portion cover. This can facilitate an operation to set a sliding-start torque. Also, in case where the adjust screw includes on the outer periphery thereof a seal member which can be slidingly contacted with the drive portion cover or the inner surface of the housing, grease filled into the cam portions of the drive shaft and hammer can be prevented from flowing out therefrom.
Preferably, in a power transmission route extending from a motor for driving to an output shaft, there can be disposed speed change means. In this case, preferably, the speed change means may be structured such that it changes the speed of power transmission in linking with the switching means and, when the drive shaft and anvil are connected by the connecting member in such a manner that they are disabled from rotating with respect to each other, executes the speed change prior to the connection between the drive shaft and anvil.
Also, in a power transmission route extending from a motor for driving to an output shaft, there may be disposed not only a torque clutch capable of switching its own operation in linking with the operation of the switching operation but also speed change means. In this case, preferably, when the anvil is held so as to be rotatable with respect to the drive shaft, the torque clutch may be removed from the power transmission route and the speed change means may provide a small speed change ratio, and, when the anvil is held so as to be disabled from rotating with respect to the drive shaft, the torque clutch may be disposed in the power transmission route and the speed change means may provide a large speed change ratio.
And, preferably, the connecting member may be structured such that it connects the drive shaft and anvil to each other only at the position where the hammer does not run onto the anvil, or such that it connects the drive shaft and anvil to each other in a state where the hammer is in contact with the anvil in a rotation transmission allowable manner.
Also, preferably, the operation allowable clearance of the connecting member in the axial direction thereof in a state where the drive shaft and anvil are separated from each other may be set larger than the thrust play of the drive shaft.
And, preferably, the operation portion and connecting member may be connected to each other through an elastic member.